Luminescent nanoparticle-based intracellular sensing

We present luminescence-based nanosensors for oxygen (O₂) and calcium ions (Ca²⁺) sensing in the cellular environment. A novel ratiometric Ca²⁺-sensitive nanoparticle (NP) consisting of a silica core coated with a shell of dextran was synthesised. A rhodamine-based reference dye was covalently bound to the silica core while the dextran shell was labelled with the Ca²⁺-sensitive probe Fluo-4. The nanoparticles have an average hydrodynamic diameter of 95 nm, good colloidal stability and show a 2.9-fold increase in fluorescence intensity upon binding to Ca²⁺ ions. The determined dissociation constant of K_d ≈ 520 nM is well suited for measurements in the physiological range. The oxygen-sensitive optical probe is the ruthenium complex [Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline), which was encapsulated in silica NPs which were synthesised using the Stöber sol-gel process. The oxygen sensitivity of the nanoparticles was measured and a calibration curve established. In addition preliminary measurements have been carried out on the introduction of the NPs into macrophages.